Appetitive olfactory learning in Drosophila larvae: effects of repetition, reward strength, age, gender, assay type and memory span

Associative plasticity is a basic characteristic of behaviour. We analysed associative olfactory learning in larval Drosophila, using a reciprocal conditioning assay. One group of animals was rewarded with fructose in the presence of odour A but not in the presence of odour B (A+/B); the companion group received reciprocal training (A/B+). During the test, larvae were given a choice between A and B; those that had received A+/B training showed a higher preference for A than reciprocally trained larvae did. As all other parameters were equal between groups, this difference was exclusively due to associative learning. Learning reached an asymptote after as few as three training trials and 2.0 mol/litre of fructose yielded asymptotic learning. Learning was not modulated by larval age tested 4, 5 and 6 days after egg laying or by gender. En masse assays confirmed the lack of gender differences. Memory was fully stable for at least 30 min. These experiments provide a basis for future investigations into the cellular and molecular underpinnings of appetitive olfactory learning in larval Drosophila.